To best explain how diesel engines work, the complete system
can be broken down into its component systems or parts.
Critical diesel components include the air intake, turbo,
wastegate, intercooler, glow plugs, fuel injection, compression
ratio.
Turbo Forced Induction
Diesel engines consume large volumes of air, greater than
an equivalent petrol engine. For non-turbo charged car the
air is simply drawn into the engine. Turbocharged diesel
cars use a turbo to compress air which forces more air into
the cylinders. This enables the engine to produce significantly
more power.
A wastegate controls the volume of air passing through
the turbo. It can detect if a turbo is spinning too fast
and acts as a safety value to limit the amount of boost
the turbo can produce. This protects both the engine and
turbo from overload.
Intercoolers
Intercoolers are necessary to cool air after it has been
compressed by the turbo. As air is compressed it heats up,
resulting in its density being reduced. If this air is not
cooled before being drawn into the engine it will produce
less power and be less efficient. An intercooler acts like
a car radiator, but in this application it cools air instead
of engine coolant / water.
Diesel Glow Plugs
Glow plugs are important for cold starting of diesel engined
cars. They are electrically controlled heaters which warm
the engine prior to cold starts. Without glow plugs, a diesel
engine would not start because the engine needs hot compressed
air to ignite injected diesel. Petrol cars do not require
glow plugs because they operate using spark plugs to ignite
a fuel/air mixture.
Diesel engines do not require complicated electronic computer
management to mix fuel and air before injection into the
cylinders. Air is compressed within the cylinder, when compressed
the air trapped inside the cylinder and combustion chamber
can reach 400-800 °C. Injectors then spray high pressure
diesel into the combustion chamber which immediately ignites
from the hot compressed air. This explosion then forces
the piston down which rotates the crankshaft, gears and
subsequently drives the wheels.
High Compression Ratios
Compression ratios are much higher in a diesel engine that
a petrol engine. High compression ratios allow diesel engines
to operate more efficiently. In a diesel engine only air
is compressed within the cylinder, so higher compression
is possible. In a petrol engine, the fuel/air mixture cannot
be compressed to such a degree because pinging or detention
occurs.